Cathode-ray tube



Dec. 12, 1950 D. E. SUNSTEIN ETAL CATl-IODE-RAY TUBE Filed Oct. 1a, 1945INVENTORS DAVID E. SUNSTE/N ARTHUR H. MA/VK/N ATTORNEYS Patented Dec.12, 1950 UNITED STATES PATENT 0 F F 1 CE 2,5333% CATHGDE-RAY TUBE DavidE. Sunste'in, (lynwyd, and Arthur H. 'Manlrin, Philadelphia, Pa,assignors, by mesne assignments, toPhilco Corporation, Philadelphia, Paa corporation of Pennsylvania Application October 18, 1945, Serial N 0..323,114

.fi claims.

Our invention relates to cathode raytubes and more particularly, to ameans for accelerating the electron beam in a cathode ray tube afterdefle c't'ion'without decreasing theamount of deflection.

In present cathode ray tubes using post-acceleration, i. -e., usingacceleration of the electron beam after the deflection of the electronbeam. there is introduced a certain amount of distortion and decrease inimage size because of the configuration of the electric field used forthis post-acceleration. In turn, the configuration of thispost-accelerating electric field is controlled by the placing orlocation of the electrode used for producing this field. In presenttubes, this is commonly manifested as a ring around the edge of the tubenear the fluorescent screen.

We 'have discovered that if a radial electric field, centered near thepoint where the electrons emerge from the deflection system, isprovided, the above-stated defects in prior-art devices are overcome.

In one embodiment of our invention, we make the entire fluorescentscreen part of the postaccelerating electrode. -However, we shape thefluorescent screen so that it will be 'part of a spherical surface thecenter of which is in the neighborhood of the deflection means used forthe electron beam. In addition, in the neighborhood of the deflectionmeans another electrode is so energized, that between the fluorescentscreen and the location of the deflection means there will be asubstantially radial electric field which will accelerate the electronbeam no matter how it is deflected by the deflecting means and will nottend to force the electron heard back to the center position of the tubeas occurs in the present means of post-acceleration.

Thus it is an object of our invention to provide post-acceleration in acathode ray tube without attendant loss of deflection.

Another object of our invention is the creation of a radial electricfield between the deflecting means and the fluorescent screen.

These objects and'other objects of our havention will be best understoodby reference to the accompanying drawing which illustrates one embodiment and which shows a cross-section oi the cathode ray tube and itsessential parts.

Referring to the drawing, the envelope of the cathode ray tube 6 is"flared out at the end opposite the electron gun "I. This electron guncreates a beam of electrons which progresses axiallythrough thetubetowards location 8. In progressing .iromgun fl to location 8; thebeam is ac-" 2 celerated'by an electric field existing between the gun Iand accelerating anode i. This electric field is produced by a source ofelectrical potential I which keeps anode l at a potential higher thanthe potential of the cathode of electron gun 1. As the electron beamapproaches location 8, it is deflected by the deflection yoke 2. Asillustrated in this figure, this is a magnetic deflection yoke and maycomprise means for the deflection or the electron beam in two mutuallyperpendicular directions. One of these directions is in the plane of thefigure and the other one is in the plane perpendicular to the figure,but still passing through the longitudinal axis of the cathode raytube.

The fluorescent screen '3, upon which the electron beam eventuallyimpinges, may be formed in a circular or spherical shape with a centerat location '8. This fluorescent screen '3 may be bordered by anelectrode located on the inside of the glass or placed inside the tubenear the fiuorescent screen. This electrode may be a separate andspecial electrode for aiding in the production of the electric fieldwill be hereinafter described, or electrode 5 may be subdivided intosegments to serve as bordering electrodes, as is described in Patent No.2,623,162, issued Sept. 19, 1950.

In addition, an external conducting shield may be placed outside of thecathode ray tube to at sist in the formation of the electric field. Thisshield 5 is so located and arranged that it is an eifective continuationof the spherical surface formed by fluorescent screen 3 and borderingelectrode 4. The geometrical configuration o1 shield 5 and the potentialapplied thereto are such as to assist in the formation of the radialfield, particularly near the edges of the fluorescent screen. Thespherical configuration shown provides this function when the glass was-6 is thin and has negligible electronic charge accumulated thereon-.Electrical connection between this shield 5 and the bordering electrodeare made by a conductor passing through the glass wall of the cathoderay tube at seal l3. Shield 5, the border electrode 4, and thefluorescent screen are all held at a potential above that of anode l bya source of potential 2, which is represented as a battery, but whichmay be any convenient means of producing such a potential.

It is well known in electrical theory that in arrangements such as shownin Figure 1, namely an electrode in the form of a spherical surface,composed of fluorescent screen 3, bordering elecfluorescent screen. Thisdistortion of the field,

however, does not extend for a very great distance beyond location 8 andconsequently any distortion in the deflection of the electron beam willnot be very great.

Inspection of these radial electric field lines will shOW that theelectron beam after deflection by deflection yoke 2 will be travellingin a direction parallel to the electric field lines. Consequently, theelectric field lines will always tend to accelerate the electron in thedirection it is moving but will not tendto give a sidewise accelerationto the electron. The result of this is that substantially no extradeflection is imparted to the electron beam. Substantially all of thedeflection which has been given to it by yoke 2 is retained as theelectron is accelerated by the electric field toward the fluorescentscreen.

Under certain circumstances, it may be desirable to cause thefluorescent screen 3 to cover most of the end of the cathode ray tubeleaving boundary electrodes 4 as rather narrow strips, Under such acircumstance, an electron beam deflected to its fullest extent mightconceivably 1;.

be subject to a distortion in the electric field except for the presenceof shield electrode 5. This shield electrode 5 insures that the edgeeffect of the electric field will occur well outside of the glassenvelope of the cathode ray tube and consequently will cause nodistortion of the electric field within the cathode ray tube.

In operation of this post-deflection means, the fluorescent screen 3,electrodes 4 and shield 5 is placed at a potential which is considerablyabove the potential of anode l. Thus members 3, 4 and 5 themselvesbecome potential anodes. For example, members 3, 4 and 5 mightconveniently be held at +5,000 volts, whereas anode i would be held at+1,000 volts both voltages being measured with respect to cathode 1.

In. order to assure the proper formation of the electric field in theneighborhood of fluorescent screen 3, it is desirable that thefluorescent screen be somewhat conducting. Thus the phosphor used in itsconstruction may be a conducting phosphor or a very thin coating ofmetal may be placed over the screen.

By using a high resistance semi-conducting phosphor, the tube can bemade flat-faced, or in general, concave or convex depending on theradial resistance pattern and the secondary emission pattern of thephosphor. It can be seen that electrons striking the phosphor will getback to the second anode by conduction, and to a lesser extent bysecondary emission, and in so doing'they will set up potentials in thephosphor which will maintain the substantially radial field in spite ofthe non-conformity of the tube face to the isopotential lines.

Our invention causes an additional practical advantage in that secondaryelectrons emitted from the fluorescent screen immediately encounter,upon their emission, an electric field of large value which tends toforce them back 4 into the fluorescent screen. In such a circumstance,the secondary electrons do not depart far enough from the spot at whichthe beam impinges to give a significant spreading of the spot. Thus ourinvention provides a means for postacceleration of electrons withoutdistortion and without spreading of the beam. I

We have described our invention with respect to a specific embodimentthereof, but we prefer to have our invention delineated by the followingclaims.

-We claim:

1. A cathode ray tube comprising an envelope, an electron gun,deflecting means, an accelerating anode, a fluorescent screen, adome-shaped electrode bordering said screen having its center ofcurvature substantially at the region of deflection of said deflectingmeans, and a shield mounted outside said tube and forming an effec--tive continuation of said screen.

2. A cathode ray tube comprising an envelope, an electron gun,deflecting means, an accelerating anode, a fluorescent screen, adome-shaped electrode bordering said screen havingits center ofcurvature substantially at the region of deflection of said deflectingmeans, said border electrode and deflecting means being held atapotential above the accelerating anode, and a shield mounted outsidesaid tube and forming an eii'ective continuation of said screen. v

3. A cathode ray tube comprising a source of an electron beam, afluorescent screen, deflecting mechanism between said source and screenfor controlling the deflection of the electron over said screen, a postaccelerating electrode located beyond said deflecting mechanism withrelation to said source and arranged to create a substantially radialelectric field from said deflecting mechanism to said screen foraccelerating said electrons, said post electrode comprising an electrodebordering said screen, and an external conducting shield forming acontinuation of said screen and connected to said bordering electrode,said last mentioned electrode and shield having a positive potentialwith respect to the portion of said tube adjacent said deflectingmechanism.

4. A cathode ray tube comprising a source of an electron beam, afluorescent screen, an accelerating electrode and deflecting mechanismbetween saidsource and screen for accelerating and controlling thedeflection respectively of the electrons of said beam over said screen,means for maintaining said accelerating electrode at a positivepotential with respectto said source of electrons, said fluorescentscreen comprising a high resistant semi-conducting phosphor and meansfor maintaining the said phosphor at a substantially high positivepotential with respect to the accelerating electrode at theregion of thetube adjacent the deflecting mechanismand forming a post acceleratingelectrode for accelerating the electrons of said electron beam afterthey have been deflected, the radial resistance pattern of thesemi-conducting phosphor screen being of a value to maintain a radialelectric field from said screen to said region at said deflectingmechanism.

5. A cathode ray tube comprising a source of an electron beam, afluorescent screen deflecting mechanism between said source and screenfor controlling the deflection of the electrons of said beam over saidscreen, means for mainta ning said region at said deflecting mechanismat a predetermined potential, said fluorescent screen comprising a highresistant semi-conducting phosphor and being maintained at a positivepotential with a respect to the region adjacent the deflectingmechanism, an anode on said fluorescent screen, the electrons strikingsaid phosphor screen, a conductive connection between said phosphorscreen and anode, said anode andphosphor screen forming a postaccelerating electrode for accelerating the electrons of said electronbeam following the deflection of said electron beam, the radialresistance pattern of the semi-conducting phosphor screen being of avalue to maintain a radial electric field from said screen to saidregion at said deflecting mechanism.

' DAVID E. SUNSTELN. ARTHUR H. MANKIN.

6 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,029,639 Schlesinger Feb. 4,1936 2,077,270 Schlesinger 1 Apr. 13, 1937 2,089,546 Dudding et a1 Aug.10, 1937 2,090,952 Schlesinger .1- Aug. 24, 1937 2,091,152 Malpica Aug.24, 1937 2,152,820 Schlesinger Apr. 4, 1939

